text:
Does the routine flown by the Thunderbirds in the F-16 feature true sustained knife-edge flight?
Does any aerobatic routine flown by the USAF Thunderbirds in the F-16 feature true sustained knife-edge flight?
By "true sustained knife edge flight" we mean that the aircraft is maintaining a constant altitude in a 90-degree bank.  It is not merely flying a ballistic trajectory, which would be manifested by the vertical speed steadily becoming less positive or more negative.
If so, is any special modification to the flight control system required to make this possible?
This question is motivated by the related ASE answer https://aviation.stackexchange.com/a/35986/34686 .

That's an interesting question.  Since the plane can fly straight up, there will be SOME angle between vertical and horizontal where fuselage lift + thrust can support the machine while moving laterally, maybe 20, or 30 or 40 degrees.  The question becomes is there enough tail power in the rudder to maintain that body AOA, whatever it is.   I've never seen any team do that sort of maneuver, and I suspect that nobody has ever tried it, so the answer is probably nobody knows.

@JohnK -- Maybe a logical extension of your point, is that "knife edge" flight is easier when climbing?  (The question is aimed at a true horizontal flight path.)

Climbing would just require more power.  Note that just about any horizontal flight path has an engine thrust component.  The thrust line just has to be above horizontal.  A regular plane in slow flight is getting maybe 5% of its lift from the vertical component of the thrust line.  A 180 HP Pitts S1 flying knife edge in level flight at a 30 deg angle is getting maybe 2/3rds of its lift from the fuselage and the rest from the prop (800lbs angled 30 deg is about a 400 lb vertical component).

Playing around with rc planes, I'm surprised how little rudder is needed to sustain knife-edge flight along a straight horizontal line.  Certainly nowhere near full in most fast-moving planes such as most electric ducted fan "jets", including the F-16.

Probably because the pitching moment the rudder has to work against to maintain a high body AOA is pretty mild.

According to the airforce instruction AFI 11-246 V1 'air force aircraft demonstration', the target entry and exit alt are at 500 Ft, with no loss of altitude expected.
The instruction applies to airforce aircraft, not only USAF Thunderbirds.

An RL HUD video of F-16 performing knife-edge starting from 0:21:

The sustained sideslip angle was close to 11 deg and just brings the flight path marker at the horizon line. The altitude was steady too, and 9770 Ft does not seems to be an airshow altitude, indicating that it's likely not a Thunderbird aircraft.


text:
Which way to turn to return to runway for downwind landing-- into crosswind or with crosswind?
The scenario-- you are taking off with a significant headwind component but also a significant crosswind component.  You experience a power loss (or perhaps a tow rope break in a glider). You judge that you are high enough to make a downwind landing on the same runway that you took off from, but not by a huge margin.
Assume that there is ample runway length downwind of you, but the runway is narrow enough that you must land on or near the centerline.  Your goal is to minimize your time in the air, and therefore your altitude lost, before you are positioned for landing, on the runway centerline and travelling downwind.
Assume you are on the extended centerline of the runway at the point of engine failure or rope break.  (Granted, there are valid reasons why it's sometimes good airmanship not to stay on the extended centerline during climbout.)
Which direction to turn initially?  Into the crosswind or away from the crosswind?  And is the answer always the same?
Please read on to better understand some of the nuances at play here--
If the crosswind component is strong enough, it is clearly best to make your initial turn into the crosswind, and to continue that turn until you are back near the runway centerline, when you'll need to make a slight reversal to align your ground track with the runway.
Intuitively it seems that if the crosswind component is lighter, there might be a case where it is beneficial to initially turn away from the crosswind component rather than into the crosswind component, to help get some lateral separation from the runway to give room to complete the turn.  Is this correct, or is this a misconception?
In more detail:

Is it ever optimal to turn away from the crosswind component and then maintain that direction of turn through the bulk of the maneuver, except for any corrections needed at the end to line up on the runway centerline?

Is it ever optimal to do an initial turn away from the crosswind component and then reverse into a turn in the opposite direction for the bulk of the maneuver?

Or is it always best to simply turn into the crosswind component and hold that turn until the maneuver is complete, except for any corrections needed at the end to line up on the runway centerline?

In the case where the crosswind component is rather light, or zero, are methods #2 and #3 essentially just two different ways to accomplish the same thing, with little difference in the outcome?

If the answer to 1) or 2) is "yes", is there a simple rule of thumb, in terms of the strength of the crosswind component, to know when either of those approaches would be optimal?

This is not meant to be a question about how the aircraft "feels" the wind in flight, i.e. about a possible risk of stalling when turning away from the wind or into the wind.  In horizontal flight, turning doesn't affect the wind the aircraft "feels".  When we are descending, the wind gradient can add or subtract energy from the aircraft depending on which direction we are flying, but for the purposes of this question, assume that the wind gradient is trivial above a wingspan or so above the ground and will have no significant effect on the outcome of the maneuver.
Once more for emphasis-- the constraints of the question are that we are trying to minimize altitude loss, not to minimize how far downwind along the runway we touch down.  If we ended up with altitude to spare after getting back to the runway, obviously we'd dump it as quickly as possible by sideslipping.  We could imagine a different scenario where we are just barely maintaining altitude with a poorly-performing engine and want to position the aircraft for a downwind landing near the upwind threshold of the runway as quickly as possible, which may well have a different optimal solution, but that's not the question that's being asked here.

Come on folks, this isn't opinion-based.  It asks which variation of the maneuver loses the least altitude, i.e. takes the least time, i.e. has the shortest flight path through the airmass.  It's a solvable problem.

Thinking it through some more, I'm pretty certain that the answer to part #1 is "no".  I guess my intuition is off, it was telling me otherwise--#3 and #4 are probably "yes"-- the problem w/ #2 may be that you have to guess how far to go before reversing the turn, which may be hard to do.

Maybe the real answer is that in a case where traffic isn't a factor, it's theoretically advantageous to hold runway heading and not stay on the extended centerline and allow the aircraft to drift w/ the crosswind some distance, at least if the wind isn't too strong-- in the event of power loss, you will be positioned to turn with simple 180 degree turn rather than "teardrop"--

I'm with @quiet flyer on this. If you're downvoting, please leave a explanation why. The question is well-posed, the answer is non-trivial and non-obvious, most pilots don't have the relevant training, and there are relevant scenarios where it can arise.

A side note: when flying radio-controlled airplanes, I do lots of downwind landings, just for fun.  I find the quickest way to get set up, immediately after an upwind takeoff, for a downwind landing that touches down near the upwind end of the runway, is to first turn away from the crosswind about 30 to 40 degrees, and then reverse into a turn in the opposite direction that is smoothly continued until the aircraft is back over the runway, pointing downwind.

(Ctd)  The aircraft is continuing to climb under power through part of this maneuver, and then at some point the throttle is cut and the turn is completed in a glide.  But in the case where the engine has failed, or the tow rope has broken, and there is a good deal of runway available in the downwind direction, I'm now agreeing with the answers that say immediately turn upwind.

(Ctd)  However, in the case where the pilot is trying to compromise between minimum altitude loss, and not touching down too far along in the downwind direction because runway length is limited, the situation seems to have more in common with the scenario I was describing above, and I wonder if there may here too be a benefit to first turning away from the crosswind and then reversing the turn.
But, that's not the case I specified in the question.  (Maybe I should ask a new question to address that scenario!)

Down-voters and close-voters-- note that this question is much more constrained, and thus much less a matter of opinion, than this highly upvoted question https://aviation.stackexchange.com/q/43202/34686 .  But, we've got some nice answers already, so guess it doesn't really matter if it gets closed--

I don't see this as being opinion based at all, there are fact based answers.

This question is definitely NOT opinion based, and there are enough good answers to prove that point.  I voted to reopen, although I don't think there is much else to say since the answers are in agreement...

Re my second June 12 comment-- meant to say "I'm now agreeing with the answers that say immediately turn toward the crosswind".

If your objective is to make a 180 and land on the runway you took off from, always turn into wind.  Less of a reverse turn to line up will be required the stronger the crosswind is, and I can't see any case where a downwind turn would make that any better since you will always end up farther off the center line than if you turn upwind, unless the crosswind component is zero.
When you fly gliders and have to be ready for rope breaks on tow, part of your mental self briefing is to note the crosswind direction and pre-plan your turn-back direction so it is into wind.  In gliders, the problem is usually not making it back; it's not overshooting after the turn back so if you are too low to complete a full circuit you must be turning into wind or you will find yourself low and abeam the mid point of the runway, the worst place to be.

John K, my flights with a self-launching glider frequently lead to a situation where a downwind turn would be preferable. It's a particular combination of a required immediate left turn/jog for noise abatement, which I exaggerate in order to put myself in a more advantageous position for an anticipated engine failure. Not saying this is common, just that it's not unthinkable

Instead of confusing yourself with crosswind and relative velocity, imagine a parallel runway you want to land on. The answer is then obvious. You always turn in the direction the runway is located
In the case it is close by, it just makes the required teardrop slightly smaller, say from turning 210° to only 190° before turning back to line up.
In case it is a bit further away, the runway is exactly in front of you after completing an approximate 180° turn (a little bit less because you need a bit of crab angle). Perfect!
In case it is really far away you will need to extend your lateral distance, either by turning 90° initially and only after a while turn to final, or by turning less than 180° and approaching the runway at an angle.
In all cases the best solution is to turn in the direction of the runway. You would never do a 270° turn in the opposite direction followed by a 90° turn to final if altitude is critical.
Going back to our crosswind example, note that a parallel runway is very much the same as a stationary runway that has moved relative to the airmass after a certain amount of time. So, always turn into the crosswind!
The only material difference is that you may want to end up in a crabbed configuration on short final to compensate for the crosswind. For a small crosswind component this is only a small factor and is probably solved with a boot of rudder. For a large crosswind you are already pointing in the right direction to approach the runway so there's no problem.
In any case, remember that your best option is probably to land straight ahead.

Getting into trivia here, but I've now convinced myself that there is no scenario in which an aircraft can end up exactly over the runway centerline after only 180 degrees of turn.  If it was correctly crabbed to stay on the extended centerline at the point of engine failure, it will always start to move past the extended centerline as it starts to turn into the crosswind, so it will always have to continue the turn past 180 degrees and fly back away from the crosswind a little bit before touchdown.  Could be the basis for a new question, as to whether this analysis is really correct--

And similarly, I'm not convinced that this situation could ever happen-- "In case it is really far away you will need to extend your lateral distance, either by turning 90° initially and only after a while turn to final,"-- again assuming that the aircraft is starting from a point on the extended centerline, and correctly crabbed to stay on the extended centerline, I don't think this situation could ever arise.  It's kind of a puzzle to think through why this should or should not be so--

@quietflyer I think you're overcomplicating things a bit. But I understand where you're coming from, in a theoretical case. However from a practical point of view, it's better to have a poorly lined up landing on the airfield than a perfect lined up landing in a tree.

@quiet flyer, regarding your first comment, if you were crabbing into the wind on upwind, and made your "180" into the wind, you could roll out after less than 180 and never cross runway centerline.  In other words, I can totally see a scenario where you remain on the upwind side of the runway, and if conditions were just right, could roll out right on centerline with the right crab established.  If conditions were just right...

Your questions are fair and there is a unique optimal response (or family of responses) to each question. It will be quite lengthy to detail all the variations, but I can at least answer some of them.
Goal state
First, we have to define what we wish to accomplish. Is the goal to be over the approach end of the runway at a reasonable height or to be down and stopped by the departure end? I would posit that a successful landing is not defined by how early the plane stops, but instead by (1) can it cross the arrival threshold while still in the air and (2) how much speed it carries over the departure end.
The conclusion is that the runway brackets our landing. Landing both too early and too late lead to 0% survival rates.
Initial conditions
Factors all of which need to be taken into account:

headwind component

The stronger the headwind, the less distance the plane travels from its starting point but also the stronger the tailwind on the downwind landing

crosswind component

The stronger the crosswind, the less(more) distance a turn upwind(downwind) carries the plane away from the airport

min sink airspeed

This establishes a maximum floor for time aloft

stall airspeed

In order to minimize the ground distance traveled in a 180 degree turn, the plane should be flying the most slowly possible, definitely below v_x.

best L/D airspeed

This is a useful indicator for determining the altitude required for a successful turnaround

climbout angle

This is mostly relevant to gliders, since their effective v_x on aerotow or winch launch is far higher than their v_y.

runway length

The longer the runway, the closer the runway end is when the engine fails.

landing distance

The plane needs to be able to stop on the runway.

Any local lift or sink.

There's a lot more +-500fpm lift/sink around than many people realize.

Topical analysis
For any given airplane, the answer completely lies in the airplane's polars. Although this is something that typically only glider pilots are trained in, which is reasonable, because engine failure is a glider pilot's de facto state. However, it means that a detailed analysis is outside the scope of this answer, since it requires background to understand how to adjust polars for headwind/tailwind and lift/sink.

Answering your questions
Let's start off by examining a 0-wind situation. In this case, the optimal maneuver is going to look something like a chandelle. The goal is to immediately exchange as much airspeed as possible for altitude and have the lowest speed possible during the 180 degree turn. Once the plane is turned around, min sink (aka v_x) or best L/D (aka v_y) might be appropriate, depending on if the problem is the runway approach end being too far or the runway departure end being too close.
(Note that this is very different from what is taught for PPL-SEL, which is first to establish min sink. That's okay, unless you're an experienced glider pilot you're probably best off not trying to optimize the solution. A stall-spin is going to finish off far worse than a landing straight ahead.)
For the purposes of your question, I'm going to assume that the winds are not more than 15% of the plane's v_y. That's a round number I pulled out of my hat because I feel the airspeed polar starts to really suffer afterwards.

Is it ever optimal to turn away from the crosswind component and then maintain that direction of turn through the bulk of the maneuver, except for any corrections needed at the end to line up on the runway centerline?

The optimal turn is the one which puts you the closest, in time, to the runway centerline. In other words, if you started the maneuver sufficiently far upwind that a 180 degree downwind maneuver left you 5 seconds from the runway centerline whereas the equivalent upwind maneuver left you 10 seconds from it, then you should turn downwind.
This could practically happen if, for noise abatement, you turned early and were already upwind when the engine failed.

Is it ever optimal to do an initial turn away from the crosswind component and then reverse into a turn in the opposite direction for the bulk of the maneuver?

Unlikely. Turning first one way and then the other is effectively an s-turn, which is what you'd want to do to burn altitude. If you are too close to the runway and do indeed need to burn some altitude then it would be better to glide a little farther away before making the 180 degree turn.

Or is it always best to simply turn into the crosswind component and hold that turn until the maneuver is complete, except for any corrections needed at the end to line up on the runway centerline?

This would be by maneuver of choice, for the reasons stated above.

In the case where the crosswind component is rather light, or zero, are methods #2 and #3 essentially just two different ways to accomplish the same thing, with little difference in the outcome?

Yes and no. If the pilot is perfect, and is already controlling the convergence to the touchdown point before even beginning the turn, then they are identical. For us mere mortals, it will be very hard to gauge being too high vs too low at that point, and so the critical facet would be to get to where the runway is in sight and made before burning altitude.

If the answer to 1) or 2) is "yes", is there a simple rule of thumb, in terms of the strength of the crosswind component, to know when either of those approaches would be optimal?

If the plane is already substantially upwind, you'd want to know how long your 180 degree turn will take, and use that to figure out if a downwind turn will leave you closer to the runway. I'd say it's somewhere in the several hundred feet range, for a small GA plane with stall speed ~60kts.
Using the formula from What is the relation between airspeed and rate of turn?, a 60kt airspeed yields (1120*tand(30)/60 = 10.8deg/s. So ~17seconds for the full 180 degree turn. At 10kts (~1000fpm) crosswind, which is already quite substantial, the downwind drift during the turn is 17/60*10000 = ~280ft. So either turn initiated parallel to, but 280' upwind from, the runway would yield identical placement to a turn started on the runway centerline with calm conditions.
And still, I would choose the upwind turn since once I'm parallel to the runway the crosswind would help me glide back inline with the runway whereas downwind I'd have to fight it.

In my question I was assuming the pilot was on the extended centerline of the runway at the point of rope break or engine failure.  Perhaps I should have stated that explicitly.  But I do appreciate the detailed analysis.

I have been advised in my self-launching glider to always let it drift crosswind immediately after takeoff, specifically in order to facilitate a return to base in case of engine failure. And at my airport, for noise abatement reasons we're required to turn 20 degrees to the left immediately upon takeoff. So it's really not uncommon at all to be off the centerline.

Re "I have been advised in my self-launching glider to always let it drift crosswind immediately after takeoff,"-- that sounds like great advice.  I do the same when flying rc airplanes just to facilitate a quicker turn around for another touch-and-go in the opposite direction.

Re "In my question I was assuming the pilot was on the extended centerline of the runway at the point of rope break or engine failure."-- I have now added that to the question.  It seemed essential not to allow the question to be too broad.  But your analysis still is of great interest, appreciate it.

You would want to turn into wind for two reasons:

The wind will push you away from the runway centerline, if you turn away from the wind then you will get pushed farther off the centerline then if you turned towards the wind. Turning to the wind means you will be in a better position to make the runway once the turn is completed, then you can let the wind push you back on the centerline on your approach. If you turn away then you have to fight the wind to get back to the runway, and you have less chance of making it
1/2mv2: that formula is for kinetic energy. If you have misjudged and you don't have enough altitude to make the turn back to the runway after all you will have to make an off-field landing and this formula becomes very important for your survival, as it tells you how much energy your airplane has if it impacts something, and the less energy your airplane has on impact the more chance you have of not dying. Let's imagine hypothetical 10 knot crosswind, and you are going into some trees as there's no field to land in. As the legend Bob Hoover advised you fly your airplane as far into the crash as possible and have it down to the slowest speed you can before impact, say just over stall speed. A Cessna 172 stalls around 43 knots, so I'll say your airspeed is 45 knots. If you turn into wind then your ground speed - which is how fast you will hit something - will be 35 knots, if you turn away from wind your ground speed will be 55 knots. To compare the relative kinetic energy we can throw away the 1/2m from the equation and just use the v2 part. 352 is 1225, 552 is 3025, which is almost 2.5 times higher, i.e. your airplane has 2.5 times more kinetic energy if you turn away from wind

Re the kinetic energy argument-- if we really want to "get down into the weeds" we could point out that if we are definitely committing to attempting to turn back to the runway, turning away from the crosswind leaves us flying slightly into the crosswind at the very end of the maneuver, while turning into the crosswind leaves us flying slightly away from the crosswind at the very end of the maneuver. I guess the latter is just a risk that we have to accept, if we decide to continue our turn further than pointing straight-into-the-wind and try to get back to the runway to land downwind.

I do agree that an initial immediate turn into the crosswind will put us in the best position to choose between returning to the runway, or landing as straight into the wind as possible.

I don't get you @quietflyer.

I'm just saying that the maneuver will end up making a "teardrop" track, so if we turn into the crosswind, we'll end up flying slightly away from the crosswind as we approach the runway.  In theory the groundspeed will be lower as we approach the runway if we've turned away from the crosswind than if we've turned into the crosswind.  (Maybe  best visualized w/ a 90-degree crosswind).

If we assume the greatest risk of landing off-runway occurs rather late in the maneuver, not early in the maneuver, then this is a one drawback of turning into the crosswind.  It's overwhelmed by other factors, but it is still a drawback.

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May a pilot take off from an outlying airport in Class E Surf area if conditions at t/o airport are above all relevant mins, but not at main airport?

Assume there is an airport at the town of "Kearny", SE of KSHR.  Assume there is no official weather reporting there.  Assume a pilot on the ground determines ceiling and visibility to be unlimited there, and also as far as he or she can see to the southeast.  May a pilot take off from Kearney under VFR (with no SVFR clearance), fly "closed circuit" around the pattern several times to shoot some touch-and-goes, and then depart to the southeast, if KSHR is reporting 1/2 mile visibility in fog?
Assume the pilot continues to experience unlimited ceiling, and visibility of at least 5 miles, at all times in actual flight.
Interested in answers based on parsing the letter of the FARs and FAA Orders, and also on answers based on actual operational practice.
Relevant:
FAR 91.155, especially parts (c) and (d)
(By the way, this is not a question about "extensions". The entire Class E "surface area" around KSHR is E2 airspace, with no E4 "extensions".)

Appears may come down to precisely which airport would be referred to by "that airport" in FAR 91.155(d)(1).

I know comments on ASE should be considered "ephemeral", but there is a comment under this answer that is relevant (at present it's the second comment there)  -- https://aviation.stackexchange.com/a/49105/34686

Also wondering why on earth some of that far outlying airspace wouldn't have been adequately protected by a "transition area" w/ Class E floor at 700' AGL-- but that's a different question--

What would lead you to believe that you might not be able to?

I’m wondering why you would even ask:  Why might the weather at airport A dictate your actions at airport B?  These sort of thought exercises must occur when filing IFR and considering the requirements for an alternate, but otherwise it’s largely irrelevant, other than situational awareness of WX in the general vicinity.  What am I missing?

@Jim - see second comment here https://aviation.stackexchange.com/a/49105/34686.  See also paragraph (near end) starting with "However" here https://aviation.stackexchange.com/a/86956/34686 -- this was in the context of transitioning through, not operating at an airport, but the point seems the same.  It seems that some controllers and some other FAA personnel view the reported weather at the main airport as being "controlling" throughout the "Surface Area" (including "extensions" if present; not a factor in the present question.)

@MichaelHall -- see my comment to "Jim" above--

The difference in the linked comment is that these FAA personnel were controlling the airspace of what is now class D.  What FAA personnel would you be required to talk to in your example who might share this interpretation, thereby limiting your decision?

@MichaelHall -- plus, obviously, if you are taking a checkride or something, you don't want to be operating contrary to the understanding of the FAA-- I'm sure we both agree that the need to talk to someone, or not, is not the controlling factor as to whether or not one should follow the regulations as they are understood by the FAA --

(should read "It was within a projecting portion of the 'control zone' for that airport, but...")

It is good to understand these things, but the regs cannot cover every conceivable scenario and FAA staffer comments are not binding.  Also, in case it helps you understand where I am coming from I have an even more extreme example than yours to offer later.  The real world scenario involves me landing under VFR at a class C airport when the weather is reported below instrument minimums.  And doing it willfully and repeatedly without being challenged...  But alas I must go to work now.

@MichaelHall -- Would like to hear more about that last!  Yes interpretations vary widely.  I've had people tell me (and I believe them) that at some airports in the past, a "Control Zone" was only considered to be "active" when weather was less than solid VFR, and at other times when "Control Zone" was "inactive" no one had a problem with, say, ultralight aircraft operating in the area (Part 103 used to prohibit ultralight flight in "Control Zones", at least without "prior authorization")-- I'm certain that that was not the actual letter of the regs but--

(Apparently airport referenced by 757toga was in fact just inside the Airport Traffic Area of the towered airport, so there was normally a requirement to talk to the tower -- see recent comments here https://aviation.stackexchange.com/a/92443/34686 -- still would say the requirement to talk to someone or not is not really the key point of interest here but good to be aware of details of specific case as best as they can be recalled-- )

it is ultimately up to the pilot to determine whether he can meet the VFR requirements.  I remember my flight instructor telling me that, for example the RVR may even be different from the pilot’s perspective at the end of the runway than from the facilities measurement location and if the pilot reasonably says he’s got the visibility he can make that decision.  The Regs certainly don’t say, “reported anywhere within the vicinity.”  And if I were flying out of Kearney I wouldn’t even have to check the weather at KSHR.

@Jim - sounds like a potential answer

I'm currently thinking that "that airport" in d1 and d2 refers to the airport at which the pilot is actually operating.  Wouldn't ground visibility always be reported for the airport for which the surface-level controlled airspace is actually designated?

I agree that Jim's comment would make a better, (at least more concise) answer, but I am going to risk DVs and TLDRs to make a point and honor what I hinted at in a comment above.
This is not so much a direct answer to the question, but is an example intended to emphasize that while it is important to know and understand the regulations we fly under as pilots, it is at least as important to discern intent so that we can exercise sound aeronautical decision making.  Regulations simply cannot cover ever possible scenario, (nor do we want them to, really...) but that doesn’t mean that we cannot, or should not, make every attempt to comply with the spirit when there are gray areas or corner cases.
To illustrate my point, let me offer a hypothetical question, and then outline a real life scenario by which you could violate the letter of the regulation while complying with the spirit.
Question:  If the primary airport served by class C airspace is reporting weather less than published instrument minimums, can I land there under visual flight rules?
The obvious answer from everyone here would be a resounding NO!  (and legally I agree…)  However, let’s examine a scenario where doing so would be no more risky than a normal landing on a CAVU day, and in fact is the preferred course of action.
Naval Air Station Whidbey Island in Washington state is located at the Northern end of the island, in a low flat area adjacent to Dugualla Bay.  Late summer and early fall weather patterns often consist of lingering high pressure which makes for the clearest flying of the year.  However, the cold waters of the Salish sea are very efficient at producing advection fog, which blankets the water as well as low lying areas persistently, especially in the morning hours.
As the sun rises it will typically burn off overland, but it isn’t uncommon for a pattern to set up for days where mid-morning the land is clear for some brief period of time until a low layer fog creeps in from the water again.  It can go on for most of the day, with fog cycling in and out like slow motion waves, from the shoreline to about the midfield intersection, and back out again.
If you note the tower location, they are on the shore side of the intersection, and there are plenty of times where the tower is completely socked in while a majority of the field is CAVU.  When the tower is socked in the weather is reported as below minimums because that's where the weather observers make their observations.
The EA-6B Prowler based at Whidbey is a single piloted aircraft, but it operated under a waiver which considered it multi piloted for USN instrument approach criteria.  This was because the side by side seating allowed the NFO to function as a copilot, monitoring instruments and assisting the pilot in acquiring the runway visually.  (Provided the NFO is qualified and current…)
Navy regs allowed multi piloted aircraft to commence an instrument approach if the weather was below reported minimums provided they had sufficient fuel to proceed to their alternate with reserves.  Single piloted aircraft were prohibited from even commencing an approach below mins. (unless it was practice only?)
Let’s get to our scenario:  An EA-6B is coming back to the field from one of the MOAs in the Eastern half of the state on a day when you can see all the way to Mount Jefferson in Oregon.  (maybe even Shasta in CA?!)  ATIS reports the ceiling is zero with visibility of a quarter mile.  Below minimums.
No problem most of the time, just stay on the IFR clearance you filed for coming home and request vectors to a visual.  Or fly an instrument procedure if you like.  Either way you already have the field in sight before you contact approach control, and you can see from over 20 miles away that it is just the far end of the runway that has shallow layer of fog sneaking in from the shoreline.  You will be at taxi speed by the time you enter it, and if you go around for any reason you will be well above it by 200’.
The problem occurred when you are an instructor pilot…  Because your right seat student NFO is not yet qualified in the aircraft you have to operate as a single piloted aircraft.  This means that you cannot commence an instrument approach when tower weather is below mins.  So, what are the legal options?

You could divert to McChord AFB and wait for the weather to report clear, launch to come home, and by the time you get there risk having the fog roll in again.  Or…

You could hold overhead a mostly clear field waiting until the weather is technically “legal”.

Both of these options felt ridiculously silly on such a nice day when most of the field is completely clear. Obviously the intent of the single pilot restriction is to prevent a weary solo fighter pilot from pressing decision height in nasty weather at the end of a long day, and being without an extra set of eyeballs to provide another margin of safety.  But options # 1 & 2 would have brought our training schedule to a screeching halt for weeks at a time during the best weather the PNW has to offer.  So, us instructor pilots would routinely exercise option #3 by calling “VMC, field in sight, Cancel IFR” and just land.
I tried numerous times to find a resolution, speaking with tower supervisors, the weather office, local FAA rep, and Navy leadership.  All had valid reasons why it was too difficult to change things to explicitly allow this, so it was just accepted.
That’s not to say the practice was understood by all, or approved.  If fact often there would be a pregnant pause on the radio, and a quizzical response from the controller.  i.e. “Confirm you have information Charlie?  Current weather is zero and a quarter, say again approach request?”
I could have simply accepted an instrument approach, because controllers were unlikely understand the limitations that bound us, or to know and care about crew qualifications.  Certain things are assumed, and not policed.
However, doing so would be an acknowledgement that I understood and agreed that the weather was IMC, and if any incident occurred it could be demonstrated that I knowingly violated the regs by commencing an approach below minimums with an unqualified crewmember in my right seat.  I felt my actions were more defensible by cancelling IFR.  By getting it on ATC audio tape that I called VMC field in sight at 20 miles I was in effect throwing the weather observation right back at them, implying “the ground conditions you report are not the actual in-flight conditions I observe directly.  (I override thee...)”  And with no prohibition against landing VFR with a student NFO, I haven’t actually violated either the letter or the spirit of any rule.
Anyway, we were taught early on to evaluate how we could justify our flying decisions if ever called on the carpet, and this one would be easy to defend.  Decisions like this should factor in probability, severity, and detectability.  I wouldn’t hesitate for a minute to take off in CAVU weather from a non-towered airport simply because another non-towered airport nearby reported some fog through a robotic system.  And I severely doubt that any regulation expressly prohibits doing so.

Obviously I would never DV for an answer being TL.  It's just a shame that there are some gray areas in the regs that have been there for 30 years and still sometimes cause pilots to fail check rides.  (Nothing directly related to the current topic.)

"Decisions like this should factor in probability, severity, and detectability." -- low detectability is probably the reason pilots flying ultralight soaring craft don't hesitate to transit the airspace "within the lateral boundaries" of Class E surface areas,  so long as many thousands of feet above the ground, though the letter of Part 103 forbids it.   I mean seriously, I'm cored out in a thermal over the high desert of eastern Washington at perhaps 6000 to 8000' AGL, and I'm going to cause a problem by flying over an airport with a Class E surface area?

(And PS some versions of the proposed rules leading up to the 1993 "alphabet" airspace re-designation actually offered some relief on this matter, one version said above 4000' AGL it was fine--)

Also low severity -- speaking of the real-world impacts on others, not the potential consequences to said pilot if some misguided soul decided to "throw the book at him"

That's... interesting to say the least. They accepted your cancellation and allowed you to proceed under VFR when the official weather observation was "zero and a quarter"? Maybe the .65 has changed since then but that sounds very strange to me. Even if you got an SVFR clearance that would be a violation of 91.157(c)(1) (which specifically references ground visibility).

I almost feel like remaining IFR, accepting a vector toward an instrument approach, reporting the field in sight and getting a visual approach clearance would be the best option from a legal standpoint. All you need for that is to "proceed visually and clear of clouds." Now I'm trying to find a reference that says the airport needs to be reporting VFR conditions in order to do a visual approach and I can't find that laid out in 14 CFR or the .65 anywhere, which I thought it was. EDIT: It is, 7–4–3b, "ensure WX conditions at the airport are VFR."

@randomhead, but a visual approach is still IFR, and I could neither commence an IFR approach, nor could I be cleared for a visual if the wx was below mins.  It's a conundrum for sure!  P.S.  I probably did a mix of things over the years.  The only thing I didn't ever do, (and I was tempted...) was to request a contact approach and come in for the overhead break.

Bear in mind I don't know exactly how the rules were written back then, but it seems to me that (strictly speaking) there was no way for you to legally get into that field. Visual approach: WX must be VFR (.65 7–4–3b). Contact approach: ground vis (ground vis!) must be 1SM (.65 7–4–6e). SVFR: ground vis must be 1SM unless an emergency exists (.65 7–5–7b & 91.157(c)(1)). Instrument approach: Violation of USN regs. The only possible out I see is you declaring an emergency and landing under SVFR.

@randomhead, yeah but declaring an emergency would have been even more silly.  It was a ridiculous situation.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
May a SVFR clearance be granted if the ceiling and visibility at the associated airport are unlimited?

The scenario-- ceiling and visibility at KSHR are unlimited, but there is an area of broken low cloud extending east from the town of Big Horn, the base of which appears to be around 900 to 1000' AGL.  In the middle of the day, a pilot preparing to depart from KSHR under VFR intends to depart to the southeast, generally following I-90, and expects that he may need to underfly this cloud layer to continue his flight, and so requests a Special VFR clearance. Is this something that ATC is authorized to grant, despite the good weather reported at the airport itself?

If the answer is "no", then what is the highest reported cloud ceiling over the airport that would allow a SVFR clearance to be granted, assuming horizontal visibility is no factor?  And could the clearance be granted if the cloud layer was only "scattered" or "few"?
(By the way, this is not a question about "extensions".  The entire Class E "surface area" at KSHR is E2 airspace, with no E4 "extensions".)
(And also not intended to be a question about safety-- assume the pilot has reason to believe the cloud layer will end shortly as the aircraft continues further southeast, and is prepared to return to the airport if it doesn't.)

A similar scenario that might perhaps be more palatable from a safety standpoint-- appears to me that the answer might be identical to (1), except for a possible issue of whether said pilot is truly unable to maintain basic VFR-- there is a band of clouds near Big Horn, and a pilot approaching KSHR from southeast under VFR in broad daylight would like to overfly the tops with less than 1000' clearance to facilitate his descent toward KSHR.  Again, ceiling and visibility at KSHR are unlimited.  May a SVFR clearance be authorized in this situation?

Please make it clear whether your answer is based on operational experience as a pilot or controller, or on a parsing of the FARs and FAA Orders, or both.  All of these types of answers are welcome.  Here's an FAA Order that is relevant-- FAA Order 7110.65Z "Air Traffic Control" -- See page 7-5-1-- download PDF here.
The fundamental purpose of this question is to ask about whether good weather at the airport will prevent a SVFR clearance from being authorized to deal with weather conditions some distance away, but still within the "surface area" designated for the airport.  I'm seeing now that there may be addition naunces around whether said conditions really cause a pilot to be unable to maintain standard VFR cloud clearance and visibility while still continuing his flight (specifically with case (2), the case where the pilot is overflying the clouds) but that's not the main thrust of the question.

(Related to https://aviation.stackexchange.com/q/345/34686 , but not a duplicate, as that question doesn't ask specifically about what happens when the weather at the airport is unlimited, and several answers imply that the weather at the airport itself must be incompatible with the cloud clearance minimums associated with standard VFR flight, in order for a SVFR clearance to be granted.

(Also similarly related to, but different from, https://aviation.stackexchange.com/a/42449/34686 .)

@MichaelHall -- yes, and the question was asked with the idea that the pilot might expect to need to underfly said cloud layer.

@MichaelHall -- ok, made some changes.  But the question is about whether the SVFR may be authorized in such a situation, not about what the pilot may do if it is authorized.

Ok, I get that.  Thanks, and it’s a good question in that regard.  Considering though that you can be cleared IFR when it is clear, is there a valid reason to believe that special VFR might be denied?  Because my assumption is that ATC would be compelled to provide you the clearance requested as long as weather is not IMC.  What you choose to do with it is on you…  Interested to see what others say.

Sounds like may end up being a deal where SVFR may be granted as long as conditions at the airport are not being reported as fully IMC?  I.e. the content on page 7-5-1 of the FAA Order "Air Traffic Control" is intended to state the worst reported weather conditions compatible with a SVFR clearance, but not to but a limit on how good the reported weather may be?

Item "b" on page 7-5-1 of the order gives the impression that the request would have to be made while the aircraft is in flight if it is a situation where the airport is reporting VFR?

@757toga etc -- Potential new question-- if there were an airport at "Kearney", and conditions there were clearly above all relevant minimums for a Class E "surface area" (say no official weather reporting, but pilot determines ceiling and visibility to be unlimited), but KSHR were reporting a ceiling at 950' AGL, could a pilot operate in the traffic pattern at Kearney under VFR without a SVFR clearance?


text:
What was the tactical purpose of the unusual flight control system that allowed the Northrop YA-9 to generate sideforce without banking?
What was the tactical purpose of the unusual flight control system that allowed the Northrop YA-9 to generate sideforce without banking?  (And, how was the system controlled by the pilot?)

(Image is public domain USAF photo, via Wikipedia)
According to Wikipedia, on the Northrop YA-9, a prototype ground attack aircraft that was a competitor with the A-10,

Split ailerons were fitted that could be used as airbrakes. When these
airbrakes were operated asymmetrically in conjunction with the
aircraft's rudder, sideways control forces could be applied (and the
aircraft moved sideways) without yawing or banking, easing weapon
aiming.

It's clear how something like this might work-- if the aircraft can be prevented (via the yaw torque generated by the asymmetrical drag created by deploying the split ailerons, on the wing opposite from the deflected rudder)  from yawing out of alignment with the instantaneous direction of the flight path, then the rudder can be used in a "backwards" sense (left rudder for a right turn) to generate sideforce and curve the flight path to the left or right, creating some change in the aircraft's heading, without banking.  Note that there would be no sideways airflow over the aircraft-- a "yaw string", if present, would stay centered, while a slip-skid ball would not.1,2
Is it a great tactical advantage to be be able to change the aircraft's heading this way rather than by banking?  Does this advantage pertain to air-to-ground gunnery in general, or only to operations at very low level, e.g. near treetop height?
Footnotes:

Note that if this conjectural description above is in fact accurate, the quoted Wikipedia article is somewhat in error-- while the aerodynamic sideforce component is not generated by yawing the nose to one side of the direction of the flight path, as it is in a conventional slip, there is a net horizontal force component, so the flight path will curve, which (due to the aircraft's "directional stability") will involve a change in heading, so the yaw rate is not zero, and the maneuver cannot be describe as being carried out "without yawing".  It's hard to imagine how the described set of flight controls could possibly be used to truly push the aircraft "sideways" through the air-- accomplishing a change in flight path with no change in heading, which would result in sideslipping flight with all its attendant aerodynamic consequences-- while also keeping the wings level.

Note also that if the objective truly is simply to allow the aircraft to move sideways through the air without changing heading, a conventional wing-down "sideslip" accomplishes that.  (And a "sideslip" is generally not described as a useful maneuver for gunnery purposes!)  Even setting aside the question of whether or not such a maneuver would really be useful, it's hard to how the described set of control surfaces could really accomplish what the Wikipedia article contends, allowing the aircraft to sideslip (changing the direction of flight path, without changing the aircraft heading) without banking at all.  The problem isn't the balance of yaw torques, but rather the fact that something must counteract the aerodynamic sideforce generated by the airflow striking the side of the fuselage.  If we can somehow increase the rudder deflection required to produce a given slip angle, we might eventually reach a point where the sideforce from the deflected rudder is strong enough to fully cancel the sideforce from the air striking the side of the fuselage.  Again, this would involve opening the split ailerons on the side opposite the deflected rudder.  But an aircraft designed to be maneuvered in this way should have a very large rudder, located only a minimal distance aft of the CG, and should have minimal fuselage side area.  The fixed vertical fin should be minimal in size-- an all-moving vertical fin with no fixed portion at all would be ideal.  Such a system could perhaps be implemented on a swept-wing flying-wing aircraft shaped something like the XB-35 or YB-49, but would seem entirely unsuited to the YA-9, with its large fuselage and large fixed vertical fin.

It's almost like the designer wanted to build a helicopter, but they put them on the wrong team.

The answer is right there in the Wikipedia text. It made aiming easier without the added complexity of banking and/or using the rudder. No reason to look for a more complicated imaginary answer. :)

"it's hard to how the described set of control surfaces could really accomplish what the Wikipedia article contends" should read "it's hard to understand how the described set of control surfaces could really accomplish what the Wikipedia article contends"

This way of controlling the flight path without banking or yawing allows for more direct control of alignment with a ground target: if you need to move sideways to line up on a given target from a specific direction, with this system you have direct proportional control of sideways velocity (and thus integral control of the sideways position): giving control input for x seconds will displace you y meters, after which you continue flying straight on target again.
In contrast, with banking and yawing you have integral control of the sideways velocity (and thus double integral control of sideways position): giving a control input for x seconds will initiate a y degree turn, after which you will be displacing at z m/s towards the position you want to achieve. To stop the movement and point at the target again, you need to bank/yaw in the opposite direction.
Now you can imagine how useful this proportional, direct control would be for lining up, especially for small corrections.
Here's some games to show how controlling position becomes more difficult with each additional integrator layer: https://github.com/partomatl/control-game or https://clixplatform.tiss.edu/phet/en/simulation/legacy/maze-game.html)

Good points, I should clarify the nomenclature in my answer. Also I agree that slipping has the same directness of control as the YA-9's special system, so the only advantage of the split aileron plus rudder is that the plane can keep the bank angle fixed, not just heading. Also I imagine this sideways "crabbing" would be a dedicated single control input, so the pilot doesn't have to worry about balancing the rudder and aileron to keep the plane heading constant. But given the marginal improvement in effectiveness over slipping might've been the reason why the system is not more common

txp -- I have a thought in reply to your last comment, but want to confirm that you will be able to see it if I post it in the chat room https://chat.stackexchange.com/rooms/138562/northrop-ya-9-sideforce-system-revisited, and that you have the capability to reply there.  Moderators want us to avoid lengthy discussions in comments in ASE --

This topic is being actively discussed in chat room https://chat.stackexchange.com/rooms/138562/northrop-ya-9-sideforce-system-revisited -- I've moved all my comments there--

Is it a great tactical advantage to be be able to change the aircraft's heading this way rather than by banking? Does this advantage pertain to air-to-ground gunnery in general, or only to operations at very low level, e.g. near treetop height?

No, and no. The proof: The A-10 also has split ailerons, and the control logic in question here could have been incorporated into it's design also, however it was not.
Had such maneuverability offered  great tactical advantages it surely would have been adopted. The Fly off between YA-9 and YA-10 (later to become the A-10) proved otherwise (from "Fairchild Republic A-10 Thunderbolt II: The 'Warthog' Ground Attack Aircraft", Peter C. Smith):

Their findings were that there was no significant difference in weapons delivery accuracy between the two prototypes.

When asked which aircraft felt right to fly, most of the test pilots opted for the YA-10. This was a vital factor due to the similarity of the delivery accuracy test results.

The Conclusions and Recommendations section specifically mentions the Side Force Control feature of YA-9, but even despite this recognition, the YA-9 lost the bid. During flight testing it did not deliver significantly different results from the traditional controls of the YA-10
Aiming with a fixed aircraft gun is not all that complex: target acquisition is just basic flying, and fine adjustments up and down is handled with aft and fore stick movement, left and right with pedals + ailerons (to keep wings level). Pedal-aileron interaction is very "grass roots" flying, and there is little sense in developing more or less complex hydromechanical systems to do special tricks. If you consider the typical shooting distance of a mile, give or take some, a very slight movement of pedals will move the impact point several meters, and very quickly.

Without a source, this statement is pure speculation. Perhaps with a FBW aircraft the system would have been implemented after all, or perhaps it was too expensive. There are 1000 different reasons why this feature was not built into the aircraft. Additionally, perhaps such a system increases the handling qualities for such a task. Again without proof, this is speculation.

Don't overdo it, it does no good for your argument. There is no source, I'll give you that, but there are no 1000 different reasons why this doohickey was not implemented. As I stated, it was not worth the hassle, if it was, it would be a feature on A-10. Aiming is easy enough without extra features as the one on the YA-9.

My point is, that the decision to adopt/not adopt a system isn't always obvious. A good example imo is the RAH 66 Commanche: It was a superior helicopter which still got stopped for a bunch of reasons.

I stand by my answer. Aiming with run of the mill controls is a no-brainer. The targets of ground attack planes are not supermaneuverable, there's no need for oddball control modes.

Interestingly, this a reaction we often encounter during the implementation of new control modes. Often especially more senior pilots comment that this or that control mode or automation is not needed because "it has always been done this way, and it worked. We do not need ". However given time and flight time with that specific system, such systems will be adopted anyways by the pilots. The pros and cons of such systems are far too complex to simply state that "there's no need, hence it is useless".

Yet the designers of F-16 stick "UI" were proven wrong :) But you are absolutely correct when we consider the introduction of the control logic of Airbus airliners, for example.

@U_flow I have added a source and citations backing up my pure speculation

Okay, "no significant difference" is a good indication that this control mode makes no difference. Nice idea though, I understand the designer of that system :).


text:
What "designs" the dihedral angle in modern airliners?
Is this an accurate description of the design process for modern jet airliners?
If not, why not?    What other factors come into play in determining the choice of dihedral angle?

Designer starts by assuming that aircraft's automated systems will maintain zero sideslip (defined as zero "yaw string" deflection) at virtually all times, except in rare cases such as when pilot is using rudder to (perhaps only partially) "kick out the crab" just before touchdown in a crosswind landing

Therefore effect of dihedral on lateral stability, yaw-roll coupling, "Dutch roll" oscillations, etc is essentially irrelevant (i.e. can be assumed to be zero, so long as the automation keeps working as described above)

Therefore choice of dihedral angle is based entirely on a) structural considerations-- what geometry is most compatible with a lightweight, strong structure and b) wingtip and engine nacelle clearance considerations-- what geometry allows adequate wingtip and engine nacelle clearance at bank angles likely to be encountered during takeoff and landing

Interesting, my approach would be completely opposite.  I.e. I would design a plane to be as inherently stable as I could possibly make it, and concede automated methods to the software folks to mitigate my shortcomings.

The consideration with airliners needs to be what happens if the computers fail. Airliners don't have ejection seats so it needs to be hand flyable in an emergency, you can't have anything that's dynamically unstable.

Yes, perhaps an airliner version of the B-2 Spirit, why not?

You don't design an aircraft for when everything is working perfectly.
So your first assumption should be assume the automated system has failed.

In hindsight this isn't really such a great question, and could have been asked more concisely-- e.g. "is the dihedral angle chosen specifically to be optimized for the situation where the yaw damper or other anti-sideslip automation is working"-- oh well.  Got lots of views!

Look at the A380: The inner engines must be high enough so they don't suck in every little piece of dirt on run- and taxiways. Therefore, the inner wing has more dihedral and the outer wing adds just enough to give sufficient dihedral effect overall. Low wing airplanes in general need some positive dihedral in order to compensate for the opposing influence of the fuselage.

A380 front view (picture source).
The tail dihedral is selected such that even with a tailstrike the tips of the horizontal tail will just stay above ground. This adds a bit dihedral effect of its own, so wing dihedral must be a bit smaller in order to produce the desired dihedral effect overall.
While Fly-by-Wire systems allow to fly unusual dihedral angles and dynamically compensate for almost any deficiencies, the regulations for airliners require them to be still flyable when the FCS has failed. Therefore, the electronics cannot remove the responsibility of the design engineers to choose the correct dihedral for agreeable flight characteristics.

That's an on-ground front view. In flight, the wings are straight.

@Koyovis, if we imagine the wingtips are deflected  up to yield a straight wing during flight, will that dihedral place the center of lift above the center of mass for this plane?

@nielsnielsen Hard to say, at first glance they look to be at about equal height, re left drawing in this link

Wouldn't landing gear strut length be more of an arbiter for engine ground clearance?

@EfeBallı one only has so much room for struts, and more importantly they are a very heavy component due to the loads they must stand. Longer strut = even more loads to manage = even heavier strut.

@EfeBallı On top of that, the A380 fuselage height was a critical parameter in development. The upper emergency exists were so high above ground that a lot of effort went into slides that could cover that. Also, people on those long slides get really fast (literally breakneck speed) that any gear length over the minimum for rotation was considered impossible.

Huh. Both are valid points. I was thinking of the 737/MAX debacle with the landing gear strut length.

@PeterKämpf -- re " The upper emergency exists were so high above ground that a lot of effort went into slides that could cover that. Also, people on those long slides get really fast (literally breakneck speed) that any gear length over the minimum for rotation was considered impossible." -- fascinating.  Time for the designers to seriously consider implementing ejection seats for passengers?  (Or bring back this idea -- https://theconversation.com/why-a-detachable-cabin-probably-wont-save-your-life-in-a-plane-crash-53532 -- could be deployed with wheels on ground, no? )

@quietflyer It will be a long way until ejection seats (or even an ejectable passenger cabin) will be seriously considered. Using the slide can be explained in a few words while using the ejection seat needs serious training. Reminds me of this funny Budget car rental ad

Designer starts by assuming that aircraft's automated systems will maintain zero sideslip (defined as zero "yaw string" deflection) at virtually all times,

Civil passenger jet design starts with making sure that any failure has no catastrophic effects. If the automated system fails, the aeroplane geometry must ensure Dutch roll behaviour that is acceptable for pilots to land the plane - with failed systems, in gusty stormy conditions, in a manner that the pilot can cope with in these difficult circumstances.
Only when it can be shown to authorities that the chance of automated system failure is smaller than $10^{9}$ flying hours, will the method in the question be allowed. Final proof will require a substantial fleet of aeroplanes making a couple of billion flying hours without total failure of the systems. In the mean while, dihedral angles will be such that good Dutch Roll behaviour is guaranteed when all automated systems are down.

The driving factor may be desired roll stability to counteract transient non zero sideslip conditions from variations in wind, weight shift of fuel or passengers, and degree of spiral stability desired.
One may start by observing dihedral built in a high wing 172 and a low wing Piper Chorokee.  Essentially, dihedral is a passive roll stability system to damp and reverse an unwanted roll force.

One can see the top graph has no stabilizing force, resulting in progressively worse stability as bank angle increases, better for hang gliders.  The bottom graph restores wings level from a minor upset if bank angle is not excessive or ailerons are not deliberately applied, better for cruising aircraft.
Yes, dihedral contributes to "dihedral effect" but serves as a roll damper$^1$.  "Dihedral effect" (to crosswinds) can be mitigated by raising vertical CG, raising the wing, or by adding side area (such as ventral fins) beneath the CG, and, as the OP suggests, flying in with "zero sideslip" as much as possible.
Additionally, with swept wings, yaw contributes to roll, so now a large vertical stabilizer is need as well and a yaw damper.  The vertical stabilizer also contributes to dihedral effect.
Perhaps we can look at the B-52 and the B-2 as a progression towards what birds do, control yaw and roll with their wings.    This does require a computer, with sufficient redundancy for safety.
$^1$  a footnote for those who feel dihedral stabilization is a "fallacy":  combined with side slip (which it creates) it is not.  The roll from a crosswind gust applies force from drag, whereas the vertical lift differential and slip effectively counteract it with straight wings.  Yaw is more of a problem with swept wings because dihedral is now counteracting lift differential (from sweep) as well as crosswind.  As dihedral alone can be insufficient, the yaw damper must be added.
Food for thought: this

outperforms this

in a crosswind!

Re "The roll from a crosswind gust applies force from drag, whereas the vertical lift differential and slip effectively counteract it with straight wings."-- are you saying that if aircraft with dihedral is struck with crosswind gust from left, the dihedral will help to prevent the aircraft from rolling to the right?  If so, the truth or fallacy of that assertion could make a new ASE question.  (I would say, "false".  The crosswind gust interacts w/ dihedral to create an unwanted difference lift between the two wings.)

(Actually, didn't you say as much in your own answer here? https://aviation.stackexchange.com/questions/80882/does-dihedral-improve-roll-stability-in-gusty-conditions/80888#80888 )

But, that's just the reaction to a gust. Doesn't mean that dihedral isn't generally stabilizing overall. And like you note, sideslip plays a critical role. (And note that the average condition of the atmosphere obviously can't be a steadily increasing gust from one direction!)

@quietflyer interestingly enough, when the gust passes the plane has absorbed some of its energy, rolling away and moving downwind. Now, it is slipping in the direction where dihedral helps it.  Also (do the math), a rolled dihedral also produces less vertical lift, so the plane also sinks.

@quietflyer it seems you are questioning the need for dihedral at all, and this is a very valid design thought.  My point is (we already have yaw dampers) why not have (safely) automated roll dampers on the wings, like birds

You said "better for hang gliders"-- here's a mind-bender (which is probably best discussed in a chat room, I may delete this comment after a bit)-- when a hang glider is flying at high speed  (low angle-of-attack) (control bar well pulled in) it shows strong spiral stability or roll stability (i.e. pilot must maintain a significant roll input toward inside of turn to prevent bank angle from decreasing)-- this is not the case at low speed (high angle-of-attack).  Yet we know that the dihedral-like effect of sweep is most pronounced at high angle-of-attack.  What on earth is going on here?

(Could be a new ASE question, I have a theory as to what the answer is but do not know for certain.)

@quietflyer  well, almost nixed my stability graphs for that thought!  Probably a combination of speed and dihedral effect from swept leading edge.  Really a great observation (from experience).  Would that suggest hang glider turns are slips?


text:
Which aircraft is easier to land-- Supermarine Spitfire or North American P-51 Mustang?
Which aircraft is easier to land (without ground-looping)-- the Supermarine Spitfire or the North American P-51 Mustang?
If the answer is different depending on conditions (e.g. no-wind versus crosswind), please elaborate.  Likewise please elaborate if a particular technique (e.g. 3-point-landing versus wheel landing) should be used to obtain the best results in a given circumstance.
Points of interest-- note that the P-51's tailwheel is located well forward of the tail, giving the landing gear a "short-coupled" configuration.  Note that the Spitfire main landing gear legs were located close together (giving a narrow "track").

I feel "easier" is in the realms of opinions

This is more a matter of opinion

I agree it's opinion-based. I suggest editing to something like What are the challenges in landing a Spitfire or P-51 Mustang? or maybe What makes the Spitfire or P-51 Mustang more difficult to land compared to other aircraft?

Hmmm maybe should I ask for published recommendations (3-point versus wheel landing) on how to land a P-51 in crosswind and no-wind conditions-- or is that too broad?  As it's likely or at least possible that not all published sources give the same recommendation--

This is more opinion based than factual. That being said I do know that the Griffon powered Spitfires were more difficult to handle in the traffic pattern due to their increased engine torque and opposite yaw effect from P-Factor of a propeller turning counterclockwise.  I know those airplanes were not popular with their pilots for that reason.  Never heard anything bad about the Merlin powered Spitfires.
Mustangs were apparently more difficult to execute good 3-point landings with and wheel landings were the recommended technique in that airplane.


text:
Do the NPRMs & Final Rules preceding 1993 "alphabet" airspace re-designation indicate that these phrases were meant to exclude Class E "extensions"?
Note-- this question is specifically about the content in the rule-making documents leading up to the September 16 1993 "alphabet" airspace re-designation, which is when the terms "Class A", "Class B", etc were introduced into the FARs, and which is also when the concept of surface-level Class E "extensions" to other surface-level controlled airspace was introduced into the FARs, and which is also when the phrases listed below were introduced into the FARs.  This question is not about any later (post 9-16-93) rulings or other issuances from the FAA.
Do the rule-making documents (including Notices of Proposed Rule-Making, and Final Rules) that the FAA published leading up to the September 16 1993 "alphabet" airspace re-designation indicate that the phrases like "within the lateral boundaries of controlled airspace designated to the surface for an airport" and "within the lateral boundaries of the surface area(s) of ... Class E airspace designated for an airport" were originally intended to exclude, or to include, surface-level Class E "extensions" (E3/E4 airspaces) to other surface-level controlled airspace?
List of some FARs potentially affected--
FAR 45.22(a)(3)(i),
FAR 65.37(f)(2), FAR 91.155(c), FAR 91.155(d), FAR 91.157(a), FAR 91.303(c), FAR 91.309(a)(4), FAR 101.33(a), FAR 103.17, FAR 107.41, FAR 121.347(a)(2), FAR 135.205(b)

The relevant rule-making documents include:
October 18 1989 Proposed Rule "Airspace Reclassification" (link to PDF of entire Federal Register issue opening to relevant page 42916)
December 17 1991 Final Rule "Airspace Reclassification" (link to PDF of entire Federal Register issue opening to relevant page 65638)
May 1 1992 Proposed Rule "Terminal Airspace Reconfiguration" (link to PDF of entire Federal Register issue opening to relevant page 18954)
August 27 1992 Final Rule "Terminal Airspace Reconfiguration" (link to PDF of entire Federal Register issue opening to relevant page 38962)

Example of surface-level Class E "extensions" to other surface-level controlled airspace (i.e. examples of E3/E3a/E4 airspaces) :
The two dashed magenta rectangles extending from the dashed blue Class D circle at KMFR--

Why this is relevant today:
Pilots should not assume that the interpretation of phrases like "within the lateral boundaries of controlled airspace designated to the surface for an airport" and "within the lateral boundaries of the surface area(s) of ... Class E airspace designated for an airport" is a settled matter, in regard to whether or not they include surface-level Class E "extensions" (E3/E4 airspaces).  At the April 2021 meeting of the Aeronautical Charting Group, high-level staffers from FAA ATO and Flight Standards divisions spoke of the ongoing confusion within the agency around this issue, and noted that pilots have failed check rides as a result.  The FAA may issue further clarification on this matter in the future.  The recent practice (only beginning in 2017, apart from one unusual earlier exception) of designating E4 surface-level Class E extensions to E2 Class E "surface areas" at untowered airports seems likely to draw increased attention to this issue-- the fact that these airspaces were not simply designated as single units of E2 airspace seems to imply that some regulatory distinction between the two airspaces may be intended, yet on aviation sectional charts the airspaces are currently charted as single units of surface-level Class E airspace.  Increased attention to potential conflicts between "drones" and full-sized aircraft may also draw further attention to the issue.  The current ambiguity clouds the interpretation of many FARs in relation to the E3/E4 "extensions" (see list above), including those relating to where a Special VFR clearance may be authorized, where VFR flight below a ceiling lower than 1000' AGL is prohibited without a Special VFR clearance, where ultralights may fly without prior authorization, where Small Unmanned Aircraft ("drones" etc) may operate without prior authorization, and more.  The ASE questions and answers, and other links, below give evidence of the FAA's lack of consistency on this matter.
Does an SVFR clearance extend to Echo surface extensions?
Does FAR 91.155c apply to class E surface extensions?
In the US, in actual practice, workload permitting, will ARTC facilities grant SVFR clearance for surface-level Class E "extensions" (E4 airspace)?
What indication has the FAA given that phrases like "surface area of Class E airspace designated for an airport" do or don't include E4 "extensions"?
What is the primary reason that the non-towered airports ACV, TVL, SGU, BIH, and SIT/PASI have E4 extensions to E2 airspace?
LAANC grid for authorization of Small Unmanned Aircraft operations-- note that the E3/E4 "extensions" are not included in the gridded areas that indicate where prior authorization is required for SUA operations.  See for example the airspace northwest of Sitka AK.  Then review the language of FAR 107.41.

"Note-- this question is specifically about the content in the rule-making documents leading up to the September 16 1993 "alphabet" airspace re-designation, which is when the terms "Class A", "Class B", etc were introduced into the FARs, and which is also when the phrases listed below were introduced into the FARs. This question is not about any later rulings or other issuances from the FAA." -- this is why this question is not a duplicate of any existing ASE question.

Would you please post a link to the rule making documents you are referring to?

You mean like internal memorandums and meeting minutes?  That’s probably subject to a FOIA request, and since the existence of such documents hasn’t been established I’m voting to close.

Well, then post a link!

Let us continue this discussion in chat.

Potential down-voters and close-voters please note-- this is why this question is not a duplicate -- https://aviation.meta.stackexchange.com/a/4312/34686

The original reason that the FAA decided to establish (E4) surface-level Class E "extensions" to Class D (or higher) airspace was unambiguously to protect the airspace to the surface, while relieving VFR pilots passing through the airspace of the need to communicate with the control tower.  From the May 1 1992 Proposed Rule "Terminal Airspace Reconfiguration", page 18958: "If these extensions were designated as Class E airspace areas, pilots who operate in the extension areas would not be required to contact the air traffic control facility having jurisdiction in those areas."  And from the August 27 1992 Final Rule "Terminal Airspace Reconfiguration", page 38964: "By designating these extension areas as Class E airspace, pilots who operate in the extension areas will not be required to contact the air traffic control facility having jurisdiction over those areas."
Keep in mind that prior to the September 16 1993 "alphabet" airspace re-organization, surface-level airspace was protected by "control zones", which after September 16 1993 were transformed into surface-level Class E airspace at untowered airports, and surface-level Class D (and higher) airspace at towered airports.  Even prior to September 16 1993, portions of "control zones" that extended beyond the basic circle around the associated airport were sometimes called "extensions", but this had no regulatory impact prior to September 1993-- these "extensions" were simply outlying portions of the "control zones".  Prior to September 16 1993, communications requirements on VFR pilots at towered airports that were not "TRSAs" or "TCAs" were not associated with "control zone" boundaries, but rather with "Airport Traffic Areas", which were circles (5 miles in radius) around all towered airports (other than TRSAs and TCAs).
After the September 16 1993 "alphabet" airspace re-designation, "Airport Traffic Areas" were abolished, and VFR pilots were required to communicate with ATC before entering Class D (or higher) airspace.  By designating outlying areas of control zones around airports with control towers as surface-level Class E "extensions" rather than as part of the Class D airspace, the airspace could continue to be protected as before, without imposing new communications burdens on VFR pilots.
Did the FAA originally intend these surface-level Class E "extensions" to be exempt from FARs that prior to September 16 1993 had simply applied to "control zones", and after September 16 1993 would contain language like "within the lateral boundaries of controlled airspace designated to the surface for an airport" or "within the lateral boundaries of the surface area(s) of Class B, Class C, Class D, or Class E airspace designated for an airport"?  (This would include FAR 45.22(a)(3)(ii), FAR 65.37(f)(2), FAR 91.155(c) (formerly FAR 91.103(c)), FAR 91.155(d) (formerly FAR 91.105(d)), FAR 91.157(a) (formerly (FAR 91.107(a)) (later modified to present form), FAR 91.303(c) (formerly (FAR 91.71(c))), FAR 91.309(a)(4), FAR 101.33(a), FAR 103.17, FAR 121.347(a)(2), and FAR 135.205(b).)
The clearest relevant content we can find in the rule-making documents leading up to the September 16 1993 "alphabet" airspace re-designation is this passage from the May 1 1992 Proposed Rule "Terminal Airspace Reconfiguration", page 18956:

Therefore, these current rules for operations in control zones would
apply to operations in the Class E airspace areas that extend upward
from the surface..., but they would not apply to operations in Class
E airspace areas that extend upward from other than the surface.**

Unless the authors of this sentence simply neglected to address the status of the surface-level Class E "extensions"-- which seems unlikely, since the one of the primary purposes of this NPRM was to introduce the surface-level Class E "extensions"--the phrase "Class E airspace areas that extend upward from the surface" must have been intended to include the surface-level Class E "extensions" as well as the core Class E "Surface Areas" that actually surround and include the airports for which they are designated.
Therefore the sentence strongly implies that the FAA's intent was that FARs that formerly had applied to the entirety of Control Zones-- including any projecting portions, which even prior to 1993, were sometimes referred to as "extensions"-- would after September 16 1993 apply to surface-level Class E "extensions", not just to core Class E "Surface Areas" that actually surround and include the airports for which they are designated.  If the May 1 1992 "Terminal Airspace Reconfiguration" NPRM or the August 27 1992 Final Rule "Terminal Airspace Reconfiguration" had intended to remove the surface-level Class E "extensions" from the scope of these FARs, that would surely have merited some discussion of the possible safety ramifications in the NPRM and Final Rule.  (See for example FAR 101.33a!)  No such discussion exists.1
It does seem unfortunate that the FAA didn't use the May 1 1992 "Terminal Airspace Reconfiguration" NPRM or the August 27 1992 "Terminal Airspace Reconfiguration" Final Rule to revise the proposed language of the FARs listed above to remove the confusing "designated for an airport" phrase.  Note that this phrase had been introduced into the proposed language of these FARs in the October 18 1989 Proposed Rule "Airspace Reclassification" and the December 17 1991 Final Rule "Airspace Reclassification", both of which entirely predate any notion of surface-level Class E "extensions" to other surface-level controlled airspace.  (At this time the FAA had planned other means of easing communications burdens on VFR pilots, such as making the Class D (and higher) surface-level airspace areas smaller than the original "control zones" wherever practical, and replacing outlying areas of "control zones" with "transition areas" with floors at 700' or 1200' AGL wherever practical.)  Therefore the "designated for an airport" phrase was clearly not originally chosen for the purpose of excluding (E3/E4) surface-level Class E "extensions".  It was simply intended to help distinguish Class E airspace that extends all the way down to the surface from Class E airspace that has a floor higher than the surface-- bearing in mind again that the selection of this phrasing entirely predates any mention of surface-level Class E "extensions" in any NPRM or Final Rule.
Note that any attempt to construe the phrase "designated for an airport" as excluding (E3/E4) surface-level Class E "extensions" causes problems with the interpretation of FAR 71.71(b), which also contains the phrase "designated for an airport": we would seem to be forced into concluding that (E3/E4) surface-level Class E "extensions" are not mentioned at all in FAR 71.71, and thus do not legally exist at all!  This is undoubtedly not the actual intent of the FAA.  FAR 71.71 is yet another FAR whose language was first proposed in the October 18 1989 Proposed Rule "Airspace Reclassification", and finalized in the December 17 1991 Final Rule "Airspace Reclassification"-- both of which entirely predate any notion of (E3/E4) surface-level Class E "extensions" to other surface-level controlled airspace. Clearly, when the (E3/E4) surface-level Class E "extensions" were finally introduced in the May 1 1992 "Terminal Airspace Reconfiguration" NPRM and the August 27 1992 "Terminal Airspace Reconfiguration" Final Rule, the significance of the "designated for an airport phrase" in the planned (effective September 16 1993) language for various FARs, including FAR 71.71(b), was a) simply overlooked, or b) judged not to exclude (E3/E4) surface-level Class E "extensions".  The latter seems more likely.
It also seems unfortunate that when the FAA published the first (effective) edition of the "Airspace Designations and Reporting Points" document, FAA Order 7400.9A, on June 16 19932, the document was organized in such a way that the phrase "designated as a surface area for an airport" was only used to describe the core (E2) Class E "Surface Areas" that actually surround and include the airports for which they are designated. Surface-level Class E "extensions" (E3, E3a, and E4 airspaces) are placed in other sections of the document, and are described by the phrase "designated as an extension".  The same structure and phrasing has been maintained in successive editions of the "Airspace Designations and Reporting Points" document all the way to the present day.  In light of the fact that, as noted above, many FARs contain the phrase "designated for an airport", and most of these same FARs also contain the phrase "surface area", this choice of structure and phrasing for the "Airspace Designations and Reporting Points" document could be construed to signify that most or all of these FARs should not be considered to apply to the (E3/E4) surface-level Class E "extensions".  And the FAA has in fact taken that position in some issuances from 2010 onwards-- for more, see the related ASE question this answer to the related ASE question "What indication has the FAA given that phrases like "surface area of Class E airspace designated for an airport" do or don't include E4 "extensions"?". But as described above, such an interpretation conflicts with the clear intent of the rule-making documents leading up to the September 16 1993 "alphabet" airspace re-designation, and also creates a problem with FAR 71.71(b).
In light of this, it seems that the FAA's choice of the language and structure for the first effective edition of the "Airspace Designations and Reporting Points" document, FAA Order 7400.9A, is best described as either a) an inappropriate rule-making action, unsupported by any actual NPRM or Final Rule, that deviated from the intent of the May 1 1992 "Terminal Airspace Reconfiguration" NPRM and the August 27 1992 "Terminal Airspace Reconfiguration" Final Rule and intentionally changed the meaning of numerous FARs by removing the (E3/E4) surface-level Class E "extensions" from the scope of these FARs, or b) sloppy authorship that was never actually intended to change the interpretation of any FAR or to remove the (E3/E4) surface-level Class E "extensions" from the scope of FARs containing language like "within the lateral boundaries of controlled airspace designated to the surface for an airport" or "within the lateral boundaries of the surface area(s) of ... Class E airspace designated for an airport".  The latter interpretation seems the more likely one.3
Footnotes:

Note that such a change would have been a deviation from the intent of the earlier December 17 1991 Final Rule "Airspace Reclassification", pre-dating the concept of the surface-level Class E "extensions", which contains the sentences (p.65648) "However, the FAA desires to continue restrictions that currently exist in the FAR on operations within control zones." and (p.65650)"There will be no decrease in safety because there is no change in the type of airspace in which ultralights are permitted to fly or operate."  Also note the extensive safety-related discussions in all four of the rule-making documents (NPRMS and Final Rules) referenced in the original question.  It seems inconceivable that if the surface-level Class E "extensions" were intended to be exempted from FARs that had formerly applied to the entirety of "control zones", there would not have been explicit discussion of the safety ramifications of this in the May 1 1992 "Terminal Airspace Reconfiguration" NPRM or the August 27 1992 Final Rule "Terminal Airspace Reconfiguration"

The June 16 1993 edition of the "Airspace Designations and Reporting Points" document, FAR 7400.9A, was actually preceded by a previous edition, FAR 7400.9, entitled "Airspace Reclassification".  This was issued November 11 1991 -- before the surface-level Class E "extensions" were conceived of -- and was slated to become effective September 16 1993.  It was replaced by 7400.9A before it ever went into effect.  It is organized slightly differently from 7400.9A, but it does contain (on page 9-132) the full text of FAR 71.71(b), as it read according to the version that at that time was slated to become effective 9-16-93.  This includes the sentence "The airspace areas listed below are designated for an airport which consist of airspace extending upward from the surface to specified altitudes, within which all aircraft operations are subject to the operating rules specified in Part 91 in this chapter."  (Italics added.)  Then--bearing the title "Control Zones at airports without Air Traffic Control Towers", follows the list of all the surface-level Class E airspaces, all of which surround and include the airports for which they are designated. (I.e., all of which constitute what we now call "E2 airspace".)  (Interestingly, in this version of the document, the phrase "surface area" is never used.)  So the language of FAR 71.71(b) is actually the real reason that the phrase "designated for an airport"  ever made it into FAA Orders 7400.9 and its successors in the first place.  With this in mind, it's inherently problematic to cite the way the "Airport Designations and Reporting Points" document (FAA Order 7400.9A and later editions) uses the phrase "designated... for an airport" as evidence that surface-level Class E "extensions" do not fall within the scope of this phrase-- because, as noted above, the same argument must logically also be extended to conclude that surface-level Class E "extensions" have been entirely omitted from FAR 71.71(b), and thus do not actually exist at all.  As noted above, this was surely not the FAA's actual intent.

It seems relevant to point out that, despite the problematic structure and phrasing of the "Airspace Designations and Reporting Points" document, each (E3/E4) surface-level Class E "extension" is in fact listed in association with the specific airport whose approaches it is designated to protect.


text:
How far in advance of "effective date" are VFR sectional charts usually made available? (US)
In the US, how far in advance of the "effective date" are new editions of VFR sectional charts usually made available?  Is the answer different for the paper version and the digital version?
Were some or all of the 2-25-2021 editions of the VFR sectional charts for US airspace released (i.e. made available) with much less "lead time" than usual?
The 2-25-21 version of the Juneau VFR sectional chart became available for downloading from the FAA's "VFR Raster Charts" web page sometime between February 3 and February 15.  Is this less "lead time" than normal?
As of today, March 1 2021, the vfrmaps.com image for Sitka Alaska (SIT/PASI) still shows the old airspace configuration, which is no longer current, due to a change published July 31 2020 and effective November 5 2020.  Here's what vfrmaps.com shows (clipped from a screenshot from this url accessed through this airnav.com link for the Sitka airport, SIT/PASI).

And here's what the airspace actually looks like, taken from a screenshot of the PDF version of the 2-25-21 Juneau sectional chart, downloaded from FAA's "VFR Raster Charts" web page-

Is it unusual for the vfrmaps.com product to still show the image from the previous edition of a VFR sectional chart, several days after the new edition has gone into effect?
And if so, is this likely related to the charts being released with less "lead time" than usual?
And if so, do similar discrepancies between commercially available on-line map products and the actual FAA charts exist in other regions of the US at present, for the same reason?
This question is not about why there were no new editions of the Juneau sectional chart issued between March 26, 2020 and February 25, 2021.  That question is asked here: Were planned release dates skipped in 2020 for the VFR sectional charts for Juneau Alaska and Dutch Harbor Alaska?

Some time in the late afternoon or evening today March 7, the vfrmaps.com image for the airspace around SIT/PASI, reached through the airnav link for SIT/PASI, was finally updated to match the 2-25-21 version of the Juneau VFR sectional chart.   That seems like an awfully long delay.  Maybe the fact that every single VFR sectional chart in the entire US was given an update effective on 2-25-21, had something to do with it?  I wonder if regions of the country suffered a similar delay in getting the vfrmaps.com charts updated?  I wonder if other commercially-available products were affected ?

According to the product catalog website of the FAA, new VFR charts are available approximately 20 days prior to their effective date. Since 25th of February 2021, the FAA releases new VFR charts every 56 days, aligned with the AIRAC cycle.

The products mentioned in this catalog are posted at Digital Products
approxiamately 20 days prior to their cycle effective dates. They are
also available through FAA Approved Print Providers.

Re "The 2-25-21 version of the Juneau VFR sectional chart became available for downloading from the FAA's "VFR Raster Charts" web page sometime between February 3 and February 15. Is this less "lead time" than normal?" and "new VFR charts are available approximately 20 days prior to their effective date"  -- it's unfortunate that I don't have a more precise idea of exactly when this chart became available-- it would seem that if it became available near February 15, that would indeed be much less "lead time" than normal--


text:
What is the correct definition of "spanwise" and "chordwise" with a swept wing?
What is the correct definition of "spanwise" and "chordwise" with a swept wing?  For example, in the context of "spanwise airflow" and "chordwise airflow"?
a) spanwise is from root to tip, generally following the quarter-chord line, and chordwise is the direction that gives the shortest distance from leading edge to trailing edge, very roughly perpendicular to the quarter-chord line.  I.e., roughly as illustrated in this related question (either diagram): Where is the spanwise flow? How does the span wise flow point the air towards the wingtip?
b) spanwise is perpendicular to the aircraft's longitudinal axis, and chordwise is parallel to the aircraft's longitudinal axis.
c) either of the above definitions could be considered to be correct, depending on the context
d) other
Not meant to be strictly multiple choice, those options are just offered as food for thought-- if one of the choices is almost right but needs some tweaking, please elaborate--
Among other things, the intent is to understand whether the diagrams linked in option a), exactly as drawn, really illustrate any net spanwise flow at all.

Related: https://aviation.stackexchange.com/q/38482/34686 , https://aviation.stackexchange.com/q/85117/34686